The present invention relates to a circular accelerator for electrons or positrons, and in particular to a small-sized circular accelerator suitable for generating synchrotron orbital radiation having high brightness and an operation method thereof.
As for conventional circular accelerators, there are synchrotron orbital radiation generators as described in technical journal, "Monthly Physics", Vol. 5, No. 11, 1984, pp. 711-721. The principle and experiment of free electron laser which converts energy of an electron beam to energy of coherent light are described in the Monthly Physics, Vol. 4, No. 5, 1983, (Whole Number 24). By using a schematic diagram of a synchrotron orbital radiation generator as shown in FIG. 2, an example of a conventional technique will now be described. An electron beam or positron beam (hereafter referred to as "electron beam or the like") emitted from a pre-accelerator 21 is injected into a storage ring by an injector system 22. The injected electron beam or the like is held on a closed orbit 28 by focusing or defocusing quadrupole magnets 26, orbit correcting steering magnets 27, and bending magnets 23. In case of a storage ring having an acceleration function, the electron beam or the like is thereafter accelerated up to desired energy in the storage ring by a high frequency accelerating cavity 25. In case the electron beam or the like is injected with desired energy, it is stored while being kept at that energy. When the electron beam or the like stored with desired energy circulates in the storage ring, the electron beam or the like emits a part of the energy as radiation 24 every time it is bent by the bending magnets 23. This radiation is used for semiconductor lithography, for example. (See JP-A-3-211817, for example.) By compensating the energy lost as a result of this emission of radiation by using the high frequency accelerating cavity 25 provided in the storage ring, the electron beam or the like having desired energy can be held on the closed orbit 28 in the storage ring. As a method for increasing the brightness of a long wavelength area of the radiation 24 emitted from the bending magnets 23 and insertion devices 18 are used. In the insertion device 18, radiations emitted from vertexes of a meandering orbit or a spiral orbit are overlapped with each other by applying an alternating field along the closed orbit 28 in the storage ring and causing a meandering or spiral movement of the electron beam or the like.
However, the insertion device must be disposed in a linear or straight orbit section where the electron beam or the like moves linearly or in a straight path. Therefore, there is a problem that a large number of insertion devices cannot be disposed in a storage ring for which a smaller size is required. That is to say, a small-sized storage ring has a small linear orbit section. In the linear orbit section, the quadrupole magnets, steering magnets, injector system, and high frequency accelerating cavity are disposed as described before. Therefore, it is impossible to raise the brightness by disposing a large number of insertion devices while maintaining the small size.
As to improvements on circular accelerators, U.S. patent application Ser. No. 07/733645 was filed on Jul. 22, 1991 (based on Japanese patent application No. 2-190543) and entitled "Circular accelerator, method of injection of charged particle thereof and apparatus for injection of charged particle thereof", and U.S. patent application Ser. No. 07/833660 was filed on Feb. 11, 1992 (based on Japanese patent application No. 3-54338) and entitled "Circular Accelerator and a Method of Injection Beams Therein". These U.S. applications are assigned to the present assignee.